Effect of 5 cm of water positive end-expiratory pressure on arterial oxygen tension in dogs during and after thoracotomy.

Thoracotomy in dogs often is associated with lower than expected arterial oxygen tensions (PaO2). Pulmonary collapse from opening the thoracic cavity is likely to be responsible for decreased PaO2 during thoracotomy. To examine whether positive end-expiratory pressure (PEEP) is beneficial to dogs undergoing thoracotomy, PaO2 and hemoglobin saturation (SaO2) were measured in dogs randomly assigned to receive 5 cm of H2O PEEP (n = 7) or no PEEP (n = 9). During surgery in both groups of dogs, PaO2 progressively decreased (P < .001), but the decrease in PaO2 was significantly less in the PEEP group (P = .027). In both groups, PaO2 did not decrease enough to have a substantial effect on SaO2. Furthermore, application of PEEP during thoracotomy did not prevent moderate hypoxemia after surgery and discontinuation of PEEP. Application of 5 cm of H2O PEEP seems to attenuate the decrease in PaO2 observed in dogs undergoing thoracotomy, but routine application of PEEP does not seem justified.